Nature of Hydration Water in (±)-Tris(ethylenediamine)cobalt(III) Chloride Hydrate, (±)-[Co(en)3]Cl3-/iH20, as Studied by *H,

The static and dynamics properties of hydration water molecules in (±)-[Co(en)3]Cl3 were studied by means of 'H, H, and , 0 solid state NMR. By 'H pulsed field gradient (PFG) NMR the apparent diffusion coefficient of mobile water through a micropore along the crystalline unique c-axis was found to be 1.0 x 10~ m s 1 . The H NMR spectrum at 141 K consists of two components, one being a Pake doublet corresponding to a quadrupole coupling constant (QCC) of (226 ± 2) kHz and an asymmetry parameter of the electric field gradient 77 of 0.08 ± 0.01, and another being a Gaussian line with a linewidth of 3.5 kHz. The 0 NMR spectrum at 300 K also consists of a narrow Gaussian peak and a broad powder pattern with a second order quadrupole effect corresponding to QCC = (6.3 ± 0.5) MHz and 77 = 0.55±0.02. The broad and narrow components are assigned to water molecules accommodated at general 12g positions and special 2a and 2b positions in the trigonal lattice with space group Plcl. From the ratio of the populations at these positions their potential energy difference was estimated to be between (2.7 ±0.1) and (3.5 ± 0.1) kJmol. The H NMR spectrum at room temperature indicates a finite quadrupole interaction which is attributable to the rapid rotation of water molecule about the molecular C2-axis. When the water content exceeds 2.7, the QCC is reduced sharply to (5.0 ±0.1) kHz at 285 K, suggesting that there occurs rapid rotation of water and rapid exchange of H between nonequivalent positions.